1. Field of the Invention
This invention relates to a data processing apparatus which transfers data from a transmission-side device to a reception-side device in response to a data transfer request from a processor and a data transfer control method applied to the data processing apparatus.
2. Description of the Related Art
In recent years, in a data processing apparatus such as a system containing a computer, a data transfer control function of automatically performing a data transfer process from a transmission-side device to a reception-side device in response to a data transfer request from a processor in order to reduce the load on the processor has been utilized. The processor can perform a process other than the above data transfer process in a period until the data transfer process is completed.
As a representative data transfer function, a direct memory access (DMA) transfer function is known.
In Jpn. Pat. Appln. KOKAI Publication No. 5-334232, there is disclosed a DMA transfer control apparatus which detects completion of a DMA transfer, provided that the number of data transfers performed becomes equal to the total number of data transfers previously specified.
However, generally, not all of the data items are always actually written into a memory controlled by the reception-side device even when data transfer to the reception-side device is completed. Therefore, in order to determine whether or not all of the data items has actually been written into the memory, it is necessary to inquire of the reception-side device about whether the write process has been completed or not. Due to the overhead caused by the inquiry, the timing at which completion of the data transfer is notified to the processor is delayed.
Therefore, it is required to realize a mechanism which efficiently notifies completion of data transfer to the processor.